Existing mission critical push-to-talk over LTE is applied to public safety applications and general commercial applications, for example, public utilities or railway applications, and supports 1-to-N (1-to-N) group communication. For 1-to-N group communication, a mission critical push-to-talk (MCPTT) system supports two media transmission modes: unicast transmission and MBMS broadcast transmission. For the MBMS broadcast transmission mode, a network architecture in which the MCPTT system is based on Group Communication System Enablers (GCSE_LTE) is shown in FIG. 1. A mission critical service server (MCS server) is an example of a GCS AS and implements management and use of broadcast bearers. An existing MCPTT server is a type of an MCS server and integrates a group communication system application server (Goup Communication System Application Server, GCS AS) function, as shown in FIG. 2. FIG. 2 shows an architecture and a function model of an MCPTT network.
An increasing quantity of services are introduced in the public safety field. To adapt to and satisfy requirements of group communication such as MCVideo and MCData, broadcast bearers need to be used to broadcast media data. A broadcast bearer service is an underlying transmission service irrelevant to a specific application layer service. In the prior art, a GCS AS function responsible for managing and using a broadcast bearer service is bound to an application layer service server, for example, an MCPTT server. In this way, each time a new service that needs to use a broadcast bearer service is introduced, the GCS AS function needs to be implemented again. As a result, an entire public safety network architecture has repetitive and coupled functions, and fast deployment of new services is hindered. Moreover, if a plurality of emergency services are configured in one group, because servers are deployed separately, it cannot be ensured that a same broadcast bearer is used for transmission for all services in a same group. There are two existing types of broadcast bearers for distributing downlink media data: a pre-established broadcast bearer and a dynamically established broadcast bearer. It should be noted that the pre-established broadcast bearer is established before a service group session is established, and the dynamically established broadcast bearer is established after a service group session is established, as shown in FIG. 3 and FIG. 4.
FIG. 3 is a flowchart of a method for pre-establishing a broadcast bearer based on an MCPTT architecture. FIG. 4 is a flowchart of a method for dynamically establishing a broadcast bearer based on an MCPTT architecture. In a process of pre-establishing or dynamically establishing a broadcast bearer based on the MCPTT architecture in FIG. 3 and FIG. 4, activation, management, and call control of the broadcast bearer are tightly coupled in an MCPTT server, resulting in relatively low efficiency of using broadcast bearer resources. A plurality of MCPTT servers may provide services in one MCPTT system, and the MCPTT servers (or GCS ASs) need to determine, based on group members (group member) that participate in a group call, whether a broadcast bearer needs to be used. In an existing MCPTT architecture, each MCPTT server manages and uses a broadcast bearer independently, and there is no system-level node that centrally controls broadcast bearers.